diff --git a/js/src/moz.build b/js/src/moz.build
index 0a4abd80f3..77acb10b9c 100644
--- a/js/src/moz.build
+++ b/js/src/moz.build
@@ -790,5 +790,5 @@ if CONFIG['GNU_CXX']:
     CXXFLAGS += ['-Wno-shadow', '-Werror=format', '-fno-strict-aliasing']
 
 # Suppress warnings in third-party code.
-if CONFIG['CLANG_CXX']:
+if CONFIG['CLANG_CXX'] or CONFIG['GNU_CXX']:
     SOURCES['jsdtoa.cpp'].flags += ['-Wno-implicit-fallthrough']